Telephone trunking-circuits.



No. 841,747. PATBN'IED JAN. 22, 1907. H. G. WEBSTER.

TELEPHONE TRUNKING CIRCUITS.

APPLICATION FILED JULY 3.1902.

3 SH ETS-SHEET l.

Q I m 5 l l mmm l m E? PATENTED JAN. 22, 19 07.

, H. G. WEBSTER.

TELEPHONE TRUNKING CIRCUITS.

APPLICATION FILED JULY3. 1902.

3 SHEETS-SHEET 2.

will

w w E E No. 841,747. PATENTED JAN. 22, 1907.

H. G. WEBSTER. TELEPHONE TRUNKING CIRCUITS.

APPLICATION FILED JULY 3.1902.

3 SHEETS-SHEET 3.

5 i W 5E 36 III-W .the Dunbar or two-wire TUTTED STATES PTENT 'OFFICE.

HARRY G. WEBSTER, OF CHICAGO, ILLINOIS, ASSIGNOR TO KELLOGG SWITCHBOARDAND- SUPPLY COMPANY, OF CHICAGO, ILLINOIS, A

CORPORATION OF ILLINOIS.

TELEPHONE TBUNKlNG-CIBCUITS.

To all whom it may concern:

Be it known that I, HARRY G. WEBSTER, a citizen of the United States,residing at Chicago, in the county of Cook andState of Illinois, haveinvented new and useful Improvements in Telephone Trunking-Circuits, ofwhich the followin is a specification.

My invention re ates to improvements in telephone trunking-circuits andapparatus whereby telephone subscribers whose lines terminate atdifferent central ofiices or central stations may be connected togetherfor conversational purposes.

In an application filed by William W. Dean, Serial No. 113,581, datedJune 28, 1902, a telephone trunking system is shown, described, andclaimed in which circuits of type are employed.

This invention relates to improvements upon the subject-matter of thesaid application of' William W. Dean; and it consists, generallyspeaking, in so constructing and arranging the apparatus thatpilot-signals common to a plurality of trunks may be employed, wherebywhen one of the trunksis used and the signals thereof operated the saidpilot-signal is also operated to more readily attract the operatorsattention to the fact that a trunk-signal has been operated.

My invention is illustrated. in the accompanying drawings, in whichFigure 1 is a diagram of subscribers lines terminating atdifierentcentral offices, with a cord-circuit at one ofiice and a trunk existingbetween said offices to connect the lines together for conversation.Fig. 2 is a diagram of a modified form of trunk. is also a diagram of amodification of the trunk which may be employed. Fig. 4 is likewise adiagram of a modified form of trunk, and Fig. 5 is also a diagram of amodification in the trunk used.

Referrin to Fig. 1, L designates one of the plurality 0% subscriberslines terminating at the central ofiice C. This line extends in twolimbs 2 and 3 from the subscribers station A to the said central ofiiceC, where it is fitted with suitable answering and multiple jacks orconnection-terminals J J At the subscribers station the usual telephoneinstruments are provided and consist of a transmitter 4, a receiver 5, aringer or call-bell 6, and the con- Specification' of Letters Patent.

Application filed July 3,1902; Serial No. 114,175. L.

Fig. 3

Patented Jan. 22, 1907.

- the receiver 5 and condenser 7 to provide a path transparent to steadycurrents, but

opaque to voice-currents. The line conductors 2 and 3 include,respectively, the armatures or springs 10 and 11 of the cut-off relay R,

which is permanently-legged to ground from the sleeve-contacts 7' 1' ofthe jacks J J The armature or spring'10 is normally connected withground through the conductor 12, while the opposite armature 11 isnormally connected with conductor 13, containing the line-relay R lorthe line, saidconductor leading to the live or ungrounded pole of thecentral battery B, the opposite pole of which is grounded. The linerelay R controls, through its armature, the circuit of the line-signalS. The forward contacts 14 and 15 of the cut-off relay R are adapted toconnect the jacks and the switchboard-section of the line with theexternal line-circuit when the said cut-off relay is energized.

At the central office 0 the usual operators cord-circuit is provided,said cord-circuit having an answering-plug P and a calling-plug Pf, eachbeing provided with a tip-contact p and a sleeve-contact 9 adaptedto-register with like contact-surfaces j and i in the jacks of the linewhen the plug is inserted therein. The tip-contacts of the plugs areconnected together by means of the tip-strands t and t of thecord-circuit and the interposed condenser 0, while the sleeve-contactsare likewise connected by the sleeve-strands s and s and the interposedcondenser 0 A conductor 16 extends from the grounded pole of the batteryB to the tip-strand t and contains the Winding, of the tip supervisoryrelay 1,

associated witli the answering-plug P, while the live pole of thebattery is connected, by means of conductor 17, with the answeringsleeve-strand s and includes the winding of the sleeve supervisory relay1' These relays r and 1 serve to control the circuit of the supervisorylamp S associated with the answering-plug P, the former relay serving tonormally close said circuit of the lamp, while I the latter relaynormally opens the same.

The battery B is associated with the opposite or calling end of thecord-circuit and is connected by conductors 18 and 19 with the tip andsleeve strands t and 8 respectively, the former conductor including thewinding of the supervisory relay 1*, while the latter conductor includesthe similar relay 1*, These relays serve in a manner similar to therelays r and r to control the circuit of the supervisory lamp Sassociated with the callingplug P v The relays r and 1' are convenientlyreferred to as the tip-relays and relays 1' and 1' as the sleeve-relays,since they are connected with and operated by current flowing over thecorresponding strands of the cordcircuit. The tip-strand t of thecalling and testing plug P is normally open through theextra spring ormovable contact of the sleeve-relay 1", but is adapted to be closed bythe said spring and its forward contact 21 when the relay is energized;The back contact 22 of this extra spring 20 is connected, through themedium of conductor 23, with one side of the high-resistance andhigh-impedance relay 1", known as the test-relay, the other side ofwhich is grounded. The armature of this relay is likewise grounded,and'its forward contact is connected with the primary winding of theoperators inductioncoil 25 by means of the conductor 24. The other endof the said primary winding is connected, through the medium ofconductor'26, to the live pole of the battery B a retardation-coil 27being included in this circuit. The operators transmitter 28 is joinedon one side to conductor 26 intermediate her primary coil and the coil27 and on the other side through conductor 29 to ground. A condenser cis' included in the operators local circuit to facilitate talking and isconnected as shown. The secondary winding of her induction-coil 25 isadapted to be included, together with herreceiver 30 and a condenser 0',ma bridge between the strands of the cord-circuit by means of anysuitable key and indicated diagrammatically by k k.

Branch connections 31 and 32 lead from opposite sides of the receiverand secondary to an order-key 1?, connected with an order circuit orwire 33, leading ti the office C A grounded alternating-currentringing-generator g is adapted to be connected, through aresistance-lamp, with the tip-strand t of the cord-circuit by means ofthe tip ringing-key spring P, the sleeve-contact k of said key beingconnected with battery-lead 26 through wire 26 and resistance 26. V

A trunk-circuit is shown extending between the central ofiices C and 0*,said trunkcircuit beingifitted at the outgoing end with multiple jac s Jand J and with a retardation-coil 34, legged to ground from the sleeveside of the circuit. The trunk extends in two limbs 35 and 36 to thecentral ofiice C,

where it is provided with suitable means for testing the condition ofthe wanted line for ringing the desired subscriber and with signals toenable the'operator to properl. attend the connection. The tip and seeve trunk-conductors 35 and 36 terminate at the incoming oflice inwindings w and w of the; repeating-coil W, and between said windings thetrunk-relay r isconnected, said relay being of high resistance. Theopposite windings 10 and w of the repeating-coil W with an interposedcondenser c are connected between the ti -strand i and the sleeve-strands 'of the flexible end of the trunk-circuit, said end being hereinafterreferred to as a trunkcord. These strands terminate in the correspondingcontacts p and p fof the trunkprlug P The tip-relay r ois legged toground om the tip-strand t of the trunk-circuit by conductor 36 andcontrols, through its spring 37 and forward contact, a short circuitcomposed of conductors 38 and 39 of the high-resistance trunk-relay W.

A sleeve-relay r is connected on one side with the live pole of thebattery B by means of conductors 40 and 41 and on the other side withthe sleeve-strand s This incoming end of the trunk is provided with atesting apparatus similar to that described for the cord-circuit at thecentral oifice C. 'The forward portion of the tip-strand t is connectedwith spring 42 of the sleeve-relay 1'", While the other portion isconnected'with the forward contact of saidspring. The back contact ofspring 42 is joined by conductor 43' with the common high-resistance andhigh-impedance test-relay r", the opposite terminal of which isgrounded. The armature of this test-rclay serves when actuated to groundone side of the operators induction-coil 44, which I winding isconnected on the opposite side with a conductor 45, containing theresistanceand impedance coil 46, and joined to conductor 47, which leadsdirectly to the live pole of the battery B The operators transcoil andthe condenser 0", are connected ermanently with the'order-circuit33, leaing to the central oflice C. The conductor 40 leads to the point 54,-from which pointthe branch-55, containing the ringing-lamp 8, leads tothe back contact v of the armature of locking-relayr, said armaturebeing connected by conductor 55 to the point 52 u on the conductor'52,ex-

-tending between t e spring 57 of tip-relay r and the front contact ofspring 51 of sleeverelay 1'", the latter spring being grounded, asshown. The conductor ,56 extends from point 54 to the front contact of sring 57 of tip-relay r and includes the win ing' of the locking-outrelay r. The forward contact of the armature of this relay isconnectedto conductor 56 at point 59 by means of conductor 58. The backcontactof spring 57 of tip-relay r is joined by conductor 59to the ay ofthe line operated during ringing.

back contact of the armature of trunk-relay 1, the forward contact ofwhich is connected by conductor 52 with the back contact of spring 51 ofsleeve-relay 1". The armature of the trunk-relay r is connected with aconductor 53, leading to the battery-wire 47 and including the guard anddisconnecting lamp S and the pilot-relay W, said latter relay serving tocontrol the circuit of pilot-signals. This incoming end of the trunk isequipped for selectivel ringing subscribers upon a party-line. tcomprises the ringing-key contacts is k and k k placed in the strands ofthe trunk-cord and adapted when actuated to suitably connect thealternating-current generator 9 with the plug P This ringing-generatorcomprises the armature 60, the grounded brush 61, the brush 62, fromwhich the alternating current is directed through the resistance-lamp 63to tip-key spring is when depressed, and brush 64 from the splitcommutator-ring, which is adapted to deliver a current of negativepulsations only through lamp 65 to the sleeve-key is when the keyis-operated. The sleeve-contact of key 1: when operated connects thesleeve of the lug to battery-lead 47 through resistance-coi 66 tomaintain the cut-ofi re- The sub'scribers lineshown in connection withthis office is of the party-line type and is connected to subscribers Dand The apparatus at these stations is similar to that at the station Aand are likewise indi-i I cated, except that the bell 6 at station D isconnected between the sleeve conductor 3 and ground, while at station Dthe bell is connected between the tip conductor 2 and ground. The sametype of normally disconnected jacks J J line-relay R cut-oif relay R,and the line-signals S are em loyed and are designated by the same reerence characters. The battery B furnishes current for the operation ofthese various relays and signals as well as for talking.

J J and J J are respectively busyback and dont-answer jacks associatedwith the incoming trunks. These circuits comprise an induction-coil 67,having its primary in circuit with a rapidly-rotating circuit-breaker68, and the battery B, this battery being preferably the same battery asB though shown separately for convenience. The secondary of theinductioncoil 67 is connected in circuit with the rapid cir-'cuit-interrupter 69 and the more slowly opcrating interrupter 70. 1 Frominterrupter busy-back jacks J through a 504011111 resistance-coil? 2,while interrupterp70 leads by conductor 73' through resistance-coil '74to the tips of the dont-a'nswer jacks. The

sleeves of both sets of jacks are'u'nite'd'by conductor75 with thegr'oundedpole of bat- The circuit-breaker 68caus'cs induced tery;currents in the secondary circuits, which are interrupted at shortintervals .by'breaker 69,

and at longer intervals by-"breaker 70 to cause distinctive tones at thejacksJ and J, "whereby when a trunk-plug is inserted in one or the otherjacks a corresponding signal is transmitted to the waiting subscriber.

In tracing the circuits hereinafter the plan of pointing out the pathfor current from the live or ungro'unded pole of the battery to theground only will be followed for convenience,-

it being understood that the return-current will seek the grounded. poleof the battery and that the circuit will therefore be coniplete.

scriber desiring a connection with a subscriber located at anotherexchange removes his receiver from the hook, and thereby closes a pathfor current between the limbs 2 and 3 of his line through thetransmitter 4 and retardation-coil 9, the condenser 7 and receiver 5being connected in parallel with the retardation-coil. The closing ofthis circuit permits current to flow from the battery B throughconductor 13, line-relay R, spring 11 of cut-off relay R, lilnb 3 of thetelephone-line, through the retardation-coil 9 and transmitter 4 at thesubstation, and

and spring 10 of cut-off relay R through conductor 12 to ground'v Theline-relay R is thus operated and closes the circuit of the si nal-lampsto ground from the conductor 13. The operator upon seeing theline-signal exposed inserts the answeringplug P into the answering-jackJ of the subscriber's line and connects her telephone 30 with the cord-,

forward contacts 14-and 15 of said armatures to the normallydisconnected jacks J J The operation or the supervisory relay r over thepath just traced serves to close through its armature and front contactthe circuit of the supervisory signal S, whichis associated with theplug P; but it is prevented from glowing by the operation of the Theoperation is as follows: The A sub- 7 thence over limb 2 back to thecentral oifice, I

The

supervisor- E signal Stherefore remains inert,

while the tip supervisory relay 1", whichis' connected in thecenducto'r- 16' andfreceives current over telephone-line and thetip-strand t of the cord circuit and through the conductor 16 to thegrounded ipole of thebatteryfB as soon'as 'the cut-ofi relay R-isoperated; Th

atteryB furnishes currentoyer the metallic telephone-line. for-theoperation of the supervisory relays and for oonversa-' tional purposes.Theoperators transm tter 28 is receiving current at sametime from- .thebattery Bover the conductor 26, through retardationcoil 27, thencethrough the trans ,mitter 28 andIOVerconduGtOr-ZQ,to hound.

"When sound-waves strike the transnntter 28,

the current fiowing therethrough is'varied,

which'caus'es-a variationof the charge in the condenser c and acorresponcurrent through the of fer 'induc.

tion-coil These induce voice-currents 'in-' the secondary, which-aretransmitted to the'line, and the operator .is-"therefore able toconverse with the calling subscriber.

'. "Upon learning that a subscriber in the exchange C is desired the Aoperatordepresses the order-key k to connect her telephone 7 with theorder wire or circuit-v 33 and rewire. The latter operator desi ates tothe peats the number of the wanted subscriber to the-B operator, whosehead-telephone is permanently connected withthe said order- A operatorthe trunk to be use for the connection and l filoceeds to test thecondition of c with the tip of the plug of thewanted the incoming trunknamed. If the line is idle, no j click will be received; but if busy thesleeve-contacts of the jacks of theline willrbe connected with thelivepole of a bat-- tery through the sleeve-obntactzand strand of theinserted plug. A complete circuit will therefore be established from thesleeve;

- contact of the tested jack, which itis assumed, is connected with thelive pole of the battery through the tip of the plug P tipstrand ispring 42, and back contact of .'sleeve-relay r conductor 43, throughthe induction-coil 44, t

connected by conductore fi through resist-- common high iresistance andimpedance test-relay or responsive device 1 to ground. This test-relaywill therefore 0 erat. and ground through its armature an front contactone side of the primary of the operator s e other side of whichis ance46 and conductor AZ'Ito the live poleof the battery B The completionofthe circuit will permit a flow of currenttherethrough, whichwillinduce a current in the set.

secondary of tlie said induction-coil and produce a clickin the receiver50 of the operators The operators receiverwill respond to this click atall-times, even though the ordercircuit should be open at the exchange,since theelectrostatic capacity of her cirsu of cuits and that of theorder-circuit'is ample for the purpose of producing the chck. In thethree-wire systems,"where the testcircuitsare insulatedjfrorn thesubscribers lines, there is no danger of varying the current fiowinginthe line'to the annoyance of the subscriber during testing; but in thetwo-wire systems, where the testing-contacts are connected directly-withthe talking-circuits, some means is necessary, or at least desirable, toprevent noticeably varying the current-'uponlines' connected forconversajtion when testing their condition at" other sections of theswitchboard. This is accomplished jin the circuit described b means ofthe test-relay 1' which is of Sue high resistance as to vary the currentupon the tested line'butsli'ghtly and which is also of high impedance,so that its current will build up slowly to thereby prevent a suddenvariation of current on the line. The subscriber or'subscribers whoselines are tested are therefore undisturbed by a sudden or largevariation of current through their instruments. .It -is apparent thatany other suitable test responslve device or indicator than the relay 10can be employed and that the operators telephone can be used in place ofthe same or in the circuit with a retardation-coil; but the arrangementdescribed is preferred. This relay is preferably common to all theincoming trunks at the one op-eiators position, as indicated by thebrane "'g lines at 43*. Upon finding the line idle the lug P is insertedin one of the multiple jac of the wanted subscribers line.

' The A operator having-received the number of the trunk to be usedinserts the callinglug P of her cord-circuit in the jackJ at er sectionof the trunk designated; The insertion of the lug P closes a circuitfromthe live pole of t ebattery B at the A office through the conductor'l9,sleeve supervisory -relay 1' sleeve-strand s v of the cord-circuit,

plug and jack, and.

sleeve-contacts of the through retardation-c011 34 to ground. This hasthe efiect of positively o erating the sleeve supervisory relay 1' w 'chattracts its armatures and cuts out the test-,

the trunk back to the 1 exchange, and thence over tip-strand t of thecord-circuit and through conductor 18, containing the winding of tipsupervisory relay 1", to the winding w andbver the ti con uctor'35 of r,and thence over the sleeve-strand s? of the opposite pole of the batteryB The closing this circuit operates the trunk-relay 1; but as theresistance of this relay is very high sufficient current does not flowthrough the tip supervisory relay 1' at the A exchange to operate thesame. The supervisory signal S associated with thecalling-plu P of theAcord-circuit, is therefore li htedy current flowin from the live pole 0'the'battery B throng conductor 26, the signal-lam S the armature andforward contact 0 sleeve supervisory relay 1- and thence through thearmature and back contact of tip supervisory relay r to ground. Thislamp is therefore lighted and remains lighted, as

hereinafter explained, until the response of,

flexible end of the trunk, through the sleevecontacts of the plug P andthe jackof the called subscriber, and thence to the cut-off relay R ofthe wanted line to ground, thus limbs of the line extending to thesubstations.

The operation of sleeve-relay r disconnects it through the spring 42 andits forward contact, and thereby establishes the circuit forconversation. It also completes the circuit of the ringing-lamp S fromthe battery B over conductor 40 to the point 54, thence over conductorand through the lamp S to the back contact. of the armature oflocking-relay r, thence through the armature and over conductor 55" tothe point52", over the conductor 52- to the front contact and armatureof sleeve-relay r to ground. The completion of this circuit causes theoperation of the ringing-lamp S and indicates to the operator that thesubscriberhas not yet responded. The operation of the trunkrelay 1" atthis time opens through its armature and back contact the circuit of theguard and disconnect-lamp S to thereby prevent its operation.

Upon the insertion of the trunk-plug P the B operator rings the wantedsubscriber. If the subscriber D is the one desired, the ringing-key k kis depressed, which throws ring ing-current upon the sleeve-strandconnected with the plug P and operates the subscribers bell over thefollowing path: from ground at the generator 9 brush 6] armature 50 ofthe generator, brush 64 through resistancelamp 65, key k thence over thesleevestrand of the cord to the plug P over the sleeve-limb 3 of thetelephone-line to the station D, and thence through condenser 7 and hell6 to ground, the receiver :5 being at this time upon the hook 8, andtherefore completing the circuit betweenthe condenser 7 and bell 6.

It will be noticed that just previous to the de ression of theringing-key k the cut-oil re ayR was receiving a negative currentthrough its coils from the battery B At the instant the ringing-key k isdepressed this path of current from the battery B is broken; but a newpath is immediately established through the relay R from the negativesource of pulsating ringin -current. The relay R is so constructed as tobe maintained in continuous'operation when this negative pulsatingcurrent is assing through its winding, and as pulsations are used .ofthe same direction as the current furnished by the battery B the relay Ris prevented from even momentarily releasing its armatures at the momentthe ringing-key was depressed.

The bell 6 at the subscribers station may be of the ordinary polarizedtype, as the presence of the condenser 7, whlch is connected directly inthe ringing-circuit, permits the operation of such a bell from thepulsating source of ringing-current. The tip-spring of ringing-key k isgrounded at this time to provide a path to ground for thereturn-currentif the subscriber should re-- spond during ringing Shouldthe sub-. scriber D be the one desired, the ringingkey is k isdepressed, which serves to conheat the generator g with the tip-strandof the cord-circuit to operate the bell at the station D a Theringing-circuit may be traced as follows: from ground at the generator 9brush 61, armature-winding 60 of the generator, brush 62, throughresistance-lamp 63, spring k in the ti -strand of the cord-circuit,thence over the tip-strand and tip-conductor 2 of the line to thestation D and thence through condenser 7 and normally closed contacts ofthe hook S and through bell 6 to ground. The bell is thus operated: Tomaintain the cut-off relay R operated during ringing, the inner contactof the sleeve-spring 7c is connected through a resistance-coil 66 withthe battery-lead 47, extending to the live pole of the battery B Thisprevents the denergization of cut-off relay R while ringing.

Since the ringing-key springs is would most often be used forordinarymetallic ringing, the return-path for current from thesubscribers station is back over the sleeve side of the line and throughthe battery B Unless, therefore, the sleeve-strand is severed at thetime of ringing the said. returncurrent will pass through the sleeve.supervisory relay 1' and cause the same to chatter, which is notdesirable. Hence the sleevespring k is arrangedito complete a by-pathfor current around said supervisory relay when ringing. It will beunderstood that a single key-lever is preferably used in the orapparatus is connected in the manner shown at A, which shows thearrangement whichl preferably use where but onesubscriber is placed uponthe line. In this case the ringing-circuit would be complete over thesubscribers' metallic circuit, the current returning to the groundedside of the ringing-generator by means of the grounded key k? orbattery-contact of the ringing-key k.

The subscriber having been called res onds by taking up his receiver,and thereby c oses a ath for current between the limbs of his me fromthe main battery B over conductors 40 and 41, sleeve strand s of theincom- I V ing end of the trunk-line 3 of the telephoneline, thencethrough retardation-coil 9 and transmitter 4 at the substation, thenceover limb 2 of the telephone-line back to the central office, and overtip-strand t of the incoming end of the trunk, including spring 42 andits forward contact f sleeve-relay-r", through conductor 36 an tip-relay1' to ground. This relay responds to this current and closesthrou h itsarmature .37 and forward con tact tie short circuit of the trunk-relay 1The resistance of the trunk-relay 1" being now removed from the path ofcurrent flowing in the trunk-circuit, the tip-relay 1* of the A cordreceives sufficient current from the battery B to operatethe same tothereby open t e circuit of supervisory signal-lamp S thus indicating tothe A operator that the Wanted subscriber has responded to his call andthat the parties are in condition to converse. Although the trunk-relay1' is now denergized and its armature engages. its back contact, theguard-lamp S is not operated, because its circuit is opened at the backcontact and spring 57 of tip-relay r". The closing of spring 57 of thetip-relay 1'? and its forward contact completes the circuit of thelockin relay 1' as follows: from the live pole o the battery B overconductor 40 to the point 54, thence through thelocking-relay 9', overconductor 56 to the forward contact and spring 57 of the relay 1",thence over conductor 52 through the forward contact and spring 51 ofsleeve-relay r to ground. The locking-relay r is therefore operated andopens through its armature and back contact the circuit of theringing-lamp S, which is extinguished and indicates to the operator thatthe called subscriber has responded to his ring. The closing of thearmature of the locking-relay upon its forward contact completes alocking-circuit for said relay from the point 59 through conductor 58,the forward contact and thearmature of the relay, conductor to point 52,and

thence over conductor 52 and the forward contact and spring '51 ofsleeve-relay 1' to ground. This circuit and the relay 1" are thereforelocked, and the ringing-lamp S is also looked out during the remainderof the connection and can only be released when the sleeve-relay 1' isdeenergized, which occurs when the plug P is pulled 0ut.-

Should the tip and sleeve contacts of the plug be crossed when the plugis inserted in a jack and the locking and other relays operated, theywill be immediately released by the opening of the sleeve-strand inringing, and no confusion would result therefrom. The subscribers arenow connected'together for conversation and the supervisory signals atboth exchanges are extinguished. The battery B is furnishing currentover the answering end of the A cord-circuit to the A subscribers linefor talking purposes and for the operation of the supervisory relays,the battery B is furnishing current over the trunk-line for theoperation of the supervisory relays associated with the answering end ofthe A cord-circuit, and the battery B is sending current over theincoming endof the trunk and to the substation D to furnish-current fortalking and for the operation of the several relays. The. voice-currentsare transmitted inductively from the subscribers line L to thetrunk-circuit through the condensers c and c in the A cord-circuit andfrom the trunk-circuit to the incoming end thereof and the subscribersline connected therewith through the medium of the repeating-coil W. Thecondenser 0 between the windings w and w of the repeating-coil at theincoming end of the trunk prevents the flow of steady currenttherethrough, but permits a free passage of the voice-currents.

At the termination of the conversation the subscribers return theirreceivers to their books, with the result, in-the case of subscriber A,that the tip su ervisory relay 1' connected with the A .001 -circuit, isdeenergized and closes, throu h its armature and ack contact, the.circuit of the supervisory signal 8*, thus indicating to the operatorthat subscriber A has returned his receiver to the hook.

When the subscriber D hangs up his teleand shows to the A operator thatthe subscriber D has hung up his receiver. The spring 57 of thetip-relay r at the incoming end of the trunk is now the circuit of thedisconnecting-lamp S and the pilot-relay 1*", said circuit being tracedfrom the live pole of the battery B tocon ductor 47, through the windingof thepilotrelay r", and through lamp 8*", thence over conductor 53, thearmature and back contact of trunk-relay r conductor 59, the backcontactand armature 57 of tip-relay 1' thence over conductor 52 to the frontcon- 'ators attention and who upon obser serted erator that the trunkhas not been connected 'The' isconnecti -lamp pilot-lamp S, Wiltherefore be'lighted, and

tact and armature 51 of the sleeve-relay 1' to ound. The operation ofthe the pilot-signal S, Whic I the lighted lamp S is thus informed thatt e A o erator has taken down the connection at t at exchange, and sheaccordingly withdraws.

the plu P from the jack of the subscribers line. pon the withdrawal ofthe trunkplug the sleeve-relay r is denergized and the circuit of thesignal-lamp S as Well as that of the pilot-relay 1, opened at the frontcontact and armature 51 of the said relay. Both lights 8 and S are thusextinguished, and at the same time the circuit oi the lockingrelay r isbroken at the same point, which relay is therefore denergized andpermits its ar-' mature to return to normal osition.

The disconnecting-signal 5 serves also as a guard-lamp in case the Aoperator inserts the calling-plug P into a wron trunk-j ack, for

the reason that the trunk-re ay of that trunk will be operated, whilethe sleeve-relay r is not. 0 erated. A circuit .will therefore be competed from the live oleof the battery B over conductor 47, t oughpilot-relay T and disconnectinglamp 8, through conductor 53, thearmature and front contact of trunk-relay 1", conductor 52", to the backcontact of spring 51 of sleeve-relay 1"", thence thr'ou h the armatureor 3 ring 51 to ground. i 3 as well as the will indicate to the operatorthat a mistake has been made. At the same time both ringing-lamp S andguard-lam S of the trunk whose plu is inwill operate, thus apprising t eopwith at its opposite end. It will be noticed that the sleeve-relayspring 51 controls,

pilot-relay r" lights attracts the operductor 75V .to ground.

through its forward contact, a ground branch from oint 52 and that fromsaid-point two 've pole of the battery, one including con-- ductor 55,the normal contacts of lockingrelay 1*, ringing-lamp S, conductors 55and 40, while the other includes conductor 52, the

. aral el paths are normally completed to the normal contacts oftip-relay 1' conductor 59,

r the normal contacts of trunk-relay 1", conductor 53, including lam Sand pilot-relay 1, and conductor 47 to t e battery. When ground isthrown upon'these parallel paths,

as by the closing of'the sleeve-relay T, which is the condition when theplug 1? of an'idle trunk is inserted in a line, both lamps are workingbefore the subscriber responds both lel path, which permits only theringing lamp to operate.

I As soon as the subscriber responds the locking-relay operates andholds open the parallel path through its contacts during the remainderof the connection. time, although the trunk-relay is no longer operated.This can only occur under these circumstances, for thereason that innormal the trunk-relay and the sleeve-relay are operated, the formerserving to open one paral- ,85

Atthe same operated, the tip-relayris opera ed, which again opens thefirst path, so that lamp S cannot glow. Now when the A operator takesdown the connection, lamp 5* operates; but

the other parallelpath remains open through locking-relay r I 111 casethe wanted -subscribers line is found busy or in case the subscriberhaving been called does not respond the plug-P is inserted in one of thejacks J or J3 and the corresponding signal istransmittedto the waitingsubscriber.

Upon inserting the P in one of the busy. back or dont-answer jacks-forexample, one of the jacks J .a path .for curcontinuity of the tip-strandt of the trunkcord through its spring 42 and the front contact. Upon thecompletion of the strand at this point the tip-relay r is provided withcurrent from thelive pole otthe generator B through'the secondary windinof the induction-coil 67, through circuit-breaker 69, and thence overconductor 71 through re sistance 72' and the tip-contacts ofthe jack andplug, and over the ti strand and.

through the relay ri'to groun This circuit is interrupted at the breaker69,'so that the relay 1? is alternately energized and deenergi zed tocorrespondingly 1n ake and break the short circuit of the trunk-relay 1which is therefore simultaneously removed from and inserted in thecircuit of the outgoing, end of the trunk. This causes the intermittentoperation of the tip-relay 1 in the A cordcircuit to effect'the flashingof the supervisory signal S whereby the A operator is not1'-- fied thatthe called-subscrrbers line is busy. 7

The flashing ofthis light of course-corre- .sponds to the rapidity ofthe breaking of the -.circuit at breaker 67 or 70, which indicates tothe operator whether the line is busyor does not answer. The subscriberis also notified by the tone caused in his receiver.

The order-circuit 33, as is indicated by the Branchinglines 33, connectsthe B operator with several A operators either at the sane or atdifl'erent exchanges.

also provided with a plurality of keys ik to The A operator is makinconnections through the medium of the or er-circuit, I do not wish to soconfine the invention, for it is apparent that the. A operator is ableby means of her testing apparatus to test the condition of the severaltrunks before her until an idle trunk is found. Uponso testin andfinding an idle trunk she may insert t e calling-plug P of hercordcircuit, with the result that the trunk-relay r operates and lightsvthe lamp 8, which lamp has been prevlously termed the guard lam'p; butin this method of operation it would act as a calling-signal from the Aoperator to. the B operator. The B operator upon seeing the signal Swould depress her listening-key k k", which would connect her receiverin series with the repeating-coil windings w and w, these receiverconnections being indicated in dotted lines in Fig. 1. She is thereforeable to communicate with the A opera-tore; The presence of th'econdensera (shown in dotted lines inparallel with the trunk-relay-r) perniit-sconversa tion between the operators at this tirre. Upon learning thedesired connection the B operator completes the same, as before. de-'scribed. It will also be understood that had the subscriberA called foraconnection with another subscriber in the same exchange the line ofthat subscriber would have been tested in the ordinary manner by meansof the cord-plug P and, the subscriber' would have been called by theringing-generator g. y

Fig. 2 shows a modificationof'the trunk' mg-circuit in which thetrunk-relay 1: is

. shunted when the tip relay operates by means of a branch containingthe repeatingcoil windings w and w, closed through the armature 37 andfront contact of the said tip-relay. It is therefore evident that whenthe tip-relay is operated the trunk-relay r is' deprived ofoperating-current. and is thus denergized, and its resistance'is removedfrom the, metallic trunk-circuit whereby the tip-relay inthe Acord-circuit operates, as described in connection with Fig. 1. Otherwisethe construction and arrangement is the same in this figure as in thatpreviously described and the operation is the same throughout. A moredetailed description of the same is therefore considered unnecessary.

Fig. 3 shows my improvements applied to a trunk in which the trunk-relayr is of low resistance and is normally connected between the sleeve side36 of the trunk-line and the ground through the repeating-coil winding'w and-thence through conductor 39 to the armature 37 and back contactto a tip-relay.

It will be seen by reference to Fig. 1 that the nccted at the other polewith the sleevestrand of the cord-circuit throu h conductor 19. Thistrunk-relay will there ore be er: ated by current from the live pole ofthe at tery B? at the A exchange over conductor 19,

sleeve-strand of the cord-circuit and sleevebattery 13 is grounded atone pole and conconductor of the trunk, and through the I trunk-relay toground. When the called subscriber responds and the tip-relay operates,as before described, a strand 37 closes on its front contact which isconnected with the tip-condudtor 35 of the trunk-line and thereforecompletes the metallic circuit of the outgoin end of the trunk. Thetrunk-relay is there ore included in this metallic portion of thecircuit; but as it is of low resistance tt does not prevent thetip-relay in the A cordcircuit. from,operatin The operation differs fromthat descrihed heretofore in that the trunk-relay is first operated overground and remains operated durin conversation of the connectedsubscribers w en the outgoing end of the trunk is closed. The operationof a disconnecting-lamp in this form of the invention does not dependupon the completion of the circuit through the back contact of thetip-relay armature, but is completed directly through the armatures ofthe trunkrelay and of the sleeve-relay, as shown, a conductor 59 leadingdirectly from the back contact of the armature of the trunk-relay to theconductor 52, extending between the spring 57 of tip-relay and theforward contact of spring 51 of the sleeve-relay. Otherwise-theoperation is the same as previously described and will beunderstoodwithout further description.

Fi .lcShOWS still anothermodification in which the trunk-relay insteadof being shortcircuited absolutely, as in Fig. 1, when the tip-relay roperates in response to the answer of the called subscriber isshort-circuited through the extra low wound relay 1", which has one sidepermanently connected with the forward contact and armature 37 of thetiprelay r and its other side permanently connected upon the sleeve sideof the winding of the trunk-relay W. This relay 1 is of suffiwhen thetip-rela operates.

' winding being in a ground branch containing the tip-relay T when therelays are operated. The ground branch ofthe tip-relay r isnormally'completed through the back contact of the armature of theauxiliary magnet- T The further operation of the system is apparent fromthe drawings and is the same as that heretofore described. Thepilot-relay and the other testing-signal operate in the same manner asin the previous figures.

Fig. 5 shows a trunk difiering slightly from Fig. 4, in which theauxiliary low-resistance relay .is omitted and the low-resistancewinding upon the trunk-relay is connected in the short circuit of thehigh resistance The operation of the system is t ought also to beapparent and is .not specifically described. The pilotrelay and thedisconnecting-lamp, as well as the'rin ing-lamp, operate over circuitscorres on ing to those of Fig. 1.

he gr heretofore reound connectlons ferred to, it will'be understood,may and in practice usuall are one and the same, or

they may be-t e common office return, al-,

though it is found by experience that it is necessary to place a deadground upon' one. side of the common battery. This ground connection maybe placed at the o posite pole of the several atteries ins tea of asshown inthe diagrams, all of which is apparent to those skilled in theart;

The pilot-relay may have one and one-half ohms resistance and the otherparts may be of the desired or usual dimensions.

Having thus described my invention, what I claim, and desire to secureby Letters Patent, is i 1. The combination with a trunk-circuit adaptedto be united to a calling-tele hone. line at its outgoing end and acalle tele phone line at its incoming end, of a plurality of relays atthe latter end of the trunk, a sig-- naling-circuit controlled by saidrelays, a

. source of current and a signaling devlce in said circuit, meanswhereby said circuit 1118'.

be void of current when no signal is displaye a ortion of the saidsignaling-circuit on one si e of the said source being used only forsignaling purposes whereby it and the said source may be common to aplurality of such trunk signaling-circuits, and a pilot signaling devicein said portion, substantially as described.

2. The combination with a trunk-circuit adapted to be united .to acalling-telephone line at its outgoing end and a calledtelephone line atits incoming end; ofa plurality oi'relays at the latter end of thetrunk, one adapted to be actuated by current over the outgoing end ofthe trunk and another over the incoming end; a signaling-circuit for thetrunk having alternate branches controlled bysaid relays and closedthereby whenever the first or second named relay is energized alone, asource of current included in said circuit, a si al actuatedwhenever thecircuit is close over either branch, a portion of the saidsignaling-circuit on one side of the source of current being used in'said circuit only whereby said portion and said source ma be common to aplurality of such trunks,

an a pilot signaling device located in such portion, substantially asdescribed.

3. The combination with atrunk-line, of a cord-circuit to connect withits outgoing end, and acalled-subscribers line having onl two wiresextending throughout the mu tiple switchboard with which its incomingend ma be connected, 9. disconnect-signalv for cuit when connection ismade with the called line for closing the circuit of said signal at onepoint, and further means operated by and during the connection of sa1dcord-circuit with the trunk for opening-theicircuit of said signal atanother point, one terminal of said signal beingfree under-said lattercondition, substantially as described.

- 4. The combination with a trunk-line, of a cord-circuit to connectwith its outgoing end, and a called-subscribers line having only twowiresextendin throughout themultiple switchboard with which its incomingend may be connected, a disconnect-signal for said incoming end, meansoperated by current flowing over a portion of the talking circuit whenconnection is made with the called line for closing the circuit'of saidsignal at one point, and further means controlled by current sent overthe trunk-circuit when the cord is connected therewith for opening thecircuit of said signal at another point, whereby said signal can only beoperated when the cord-circuit is disconnected from the trunk, oneterminal of said signal being free in said latter position,substantially as described. r v

5. The combination with a trunk-line, of a cord-circuit to connect withits outgoing end, and a called-subscribers line having only two wiresextending throughout the multiple switchboard with which its incomingend .may be connected, a disconnect-signal 'for said incoming end, meansactuated by current flowing over a part of the talkin -circuit whenconnection is established with t e called line for closing the circuitof said signal at one point to place it in condition to operate, andfurther means operated by the connection of said cord-circuit with thetrunk for opening the circuit of said signal at another point, renderingthe same inoperative with- 'sai incoming end, means 0 erated by currentflowing over a portion 0 the talking-cirout placing a shunt about saidsignal, substantially as described.

6. The combination with a trunk-line, of a cord-circuit to connect withits outgoing end, and a called-subscriber's line having only two wiresextending throughout the multiple switchboard with which its incomingend may be connected, a disconnect-signal for said incoming end, a'relayactuated by current flowing over a portion of the talkingcircuit forclosing the circuit of said signal at one point and placing it incondition to operate, and a trunk-relay at the incoming end of the trunkadapted to be actuated when a connection is established between thecordcircuit and the trunk to open the circuit of said signalat a secondpoint, rendering the same inoperative without placing a shunt about saidsignal, substantially as described.

7. The combination with a trunk-line, of a cord-circuit to connect withits outgoing end and a calledsubscribers line having only two wiresextending throughout the multiple switchboard with which its incomingendmay be connected a disconnect-si 'nal for said incoming end, a relayactuate over a portion of the talking-circuitwhen connec tionis madewith the called line forclosing the circuit of said signal at one point,and a trunk-relay at the incoming end of the trunk actuated by currentfrom the cord-circuit when the cord is connected with the trunk to openthe circuit of said signal at another point, one terminal of said signalbeing left free under said latter condition, and a pilotrelay adapted tobe actuated in series with said si nal, substantially as described.

8. T e combination with a trunk-line, of

a cord-circuit to connect with its outgoing end, and acalled-subscribers line having only two wires extending throughout themultiple switchboard with which its incoming end may be connected, adisconnect-signal for said incoming end having its circuit closed bycurrent flowing over a portion of the talking-circuit when a trunk isconnected with the called line, and means depending upon the connectionof the cord with the trunk to again open the circuit of said signal atan.- other point, the contacts in the circuit of said signal being bothon the same side of the signal, and a pilot-relay connected in serieswith a plurality of said signals, substantially as described.

9 The combination with a'trunk-line, of a cord-circuit to connect withits outgoing end, and a called-subscribers line having only two wiresextending throughout the multiple switchboard with which its incomingend is connected, a disconnect-signal for the incoming end of the trunk,and a pilot-relay in series with said disconnect-signal, means operatedover one side of the talking-circuit to close thecircuit of said signalwhen the trunk is connected with the called line, a trunk-re lay also.at the incoming end of 'the trunk actuated when the oordcircuit isconnected with the trunk, the said trunk-relay servingto open thecircuit of said signal at asecond point when the cord is connected withthe trunk, and to close the same when the cord.- circuit is disconnectedtherefrom, thecontacts of said signal-circuit being' both on the sameside of the signal, whereby a plurality of'said signals associated withdifferent trunk-circuits may be connected in series with saidpilot-relay, substantially as described.

1D. The combination with a trunk-line, of a cord-circuit to connect withits outgoing end, and a called-subscribers line with which its incomingend is adapted to be connected, a guard-signal for the incoming end ofthe trunk, means to close the circuit of said signal by current flowingover the two limbs of the trunk-line in series when the'oordcircuit isconnected with the trunk, and further means actuated by current sentover a portion of the talking-circuit when the trunk is connected with acalled line for opening the circuit of said signal at another point, thesaid points being located in the signal-circuit on the same side of saidsignal, and a pilotrelay permanently connected in series with saidsignal, substantially as described.

11. The combination With a trunk-line, of a cord-circuit to connect withits outgoing end, and a called-subscribers line with which its incomingend is adapted to be connected, a guard-signal for the incoming end ofthe trunk, a relay adapted to close the circuit of said signal at onepoint, and adapted to be actuated over a portion of the talking-circuitwhen the incoming end of the trunk is connected with thecalled-subscribers line, said relay having its coil out of the path ofvoice-currents, a trunk-relay connected with the outgoing end of thetrunk and adapted to be actuated by current flowing over the two asecondpoint, and means for actuating said signal when the first-named relay isdeenergized and the trunk-relay is energized, the

contacts in the circuit of saidsignal being both on the same side ofthesigna-L'and a VVM. W. DEAN, i i G. Bnn'nn.

